Is there any information about additive animations?

[Shiagur42]

The title says it all but hey, there is a big empty box here that I might as well fill.

I'm currently working on a weapon mod with custom animations based on the vanilla syringer and a Blender rig for animations plus an accompanying guide for people who want to make their own animations. 

The regular animations like reloading, melee, etc. work perfectly fine and I can export them without any problems. The aiming animation, however, was causing me some trouble. Even with no movement at all, the sight slowly crawled up the screen over the course of several minutes. That I could fix by replacing the additive animation WPNIdleSightedWobble.hkx with a perfectly still animation. Now nothing moves anymore and aiming doesn't break.

Now I want to properly replace the additive animation with a properly made one, but I can't find anything about them on the internet. I know there is a filter for creating additive animations in the Havok filter manager tool, and I've managed to make a swaying animation, with a greatly overexaggerated animation, but I feel like there must be a better way.

So my question is, do any of you fine people know anything about or can point me in the direction of information on additive animations?

EDIT: my forum post here is the first result when you Google "havok additive animations" lol